Method and apparatus to automatically maintain loop isolation in position variant MRI coils

Abstract

An RF coil loop assembly technique that maintains coil isolation at varying coil positions is presented. A mutual inductance compensation circuit connected in series with each RF coil loop of the coil loop assembly substantially minimizes the coupling, or mutual inductance, that forms between the RF coil loops. The mutual inductance of the compensation circuit substantially equals, and is opposite in phase or polarity, to the mutual inductance that forms between the RF coil loops as the RF coil loops move or rotate with respect to each other.

1. An RF coil assembly comprising:
 a pair of RF coils movable with respect to one another;  
 a first inductor assembly in series with one RF coil;  
 a second inductor assembly in series with the another RF coil; and  
 wherein the inductor assemblies are configured to have a mutual inductance opposite in polarity arid substantially equal in magnitude to a mutual inductance of the pair of RF coils.  
 
     
     
       2. The RF coil assembly of  claim 1  wherein the inductor assemblies are configured to cancel the mutual inductance of the pair of RF coils with varying relative position of the pair of RF coils as long as the first and second inductor assemblies overlap. 
     
     
       3. The RF coil assembly of  claim 2  wherein the RF coils in the pair of RF coils are movable alone at least one of an x-axis, a y-axis, and a z-axis. 
     
     
       4. The RF coil assembly of  claim 3  wherein the RF coils in the pair of RF coils are rotatable about an axis of rotation. 
     
     
       5. The RF coil assembly of  claim 3  wherein the RF coils in the pair of RF coils are translatable along an imaging plane. 
     
     
       6. The RF coil assembly of  claim 1  wherein the inductor assemblies collectively have a mutual inductance opposite in phase to that of the pair of RF coils. 
     
     
       7. The RF coil assembly of  claim 1  wherein the mutual inductance of the inductor assemblies varies with RF coil positioning in a manner to cancel the mutual inductance of the pair of RF coils. 
     
     
       8. The RF coil assembly of  claim 7  wherein the mutual inductance of the indicator assemblies decreases as a distance between the pair of RF coils increases and increases as the distance between the pair of RF coils decreases. 
     
     
       9. The RF coil assembly of  claim 1  wherein the inductance of the inductor assemblies is such that coupling of the pair of RF coils is reduced regardless of coil position. 
     
     
       10. The RF coil assembly of  claim 1  incorporated into an MRI system having a magnetic resonance imaging (MRI) system having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images. 
     
     
       11. An MRI apparatus comprising:
 a magnetic resonance imaging (MRI) system having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images, the RF coil assembly comprising: 
 a first moveable coil loop;  
 a second moveable coil loop;  
 a mutual inductance compensation circuit connected to the first and the second moveable coil loops; and  
 wherein the compensation circuit is constructed to generate an inductance that minimizes a coupling of the first and the second coil loops independent of coil loop position relative to one another.  
 
 
     
     
       12. The MRI apparatus of  claim 11  wherein the mutual inductance compensation circuit is constructed such that the generated inductance is opposite in polarity and substantially equal in magnitude to mutual inductance of the first and second coil loops. 
     
     
       13. The MRI apparatus of  claim 12  wherein the inductance generated by the mutual inductance compensation circuit varies with position of the first moveable coil loop and the second moveable coil loop relative to one another. 
     
     
       14. The MRI apparatus of  claim 11  wherein the first moveable coil loop and the second moveable coil loop are movable with respect to each other along at least one of an x-axis, a y-axis, and a z-axis. 
     
     
       15. The MRI apparatus of  claim 14  wherein at least one of the first moveable coil loop and the second moveable coil loop is rotatable about an axis of rotation. 
     
     
       16. The MRI apparatus of  claim 15  wherein the mutual inductance compensation circuit is constructed to increase the inductance generated as a relative angle of the first moveable coil to the second moveable coil increases in magnitude. 
     
     
       17. The MRI apparatus of  claim 11  wherein the first moveable coil loop and the second moveable coil loop collectively form a coil for acquiring MR data of a region of a patient. 
     
     
       18. The MRI apparatus of  claim 11  wherein the mutual inductance compensation circuit includes a first inductor in series with the first moveable coil loop and a second inductor in series with the second moveable coil loop. 
     
     
       19. A method of manufacturing an RF coil assembly comprising the steps of:
 connecting a first inductor assembly in series with a first RF coil;  
 connecting a second inductor assembly in series with a second RF coil; and  
 calibrating the first inductor assembly and the second inductor assembly such that a mutual inductance therebetween substantially isolates the first and the second RF coils independent of coil position relative to one another.  
 
     
     
       20. The method of  claim 19  wherein the mutual inductance of the first and the second inductor assemblies is opposite in polarity and substantially equal in magnitude to a mutual inductance of the first and the second RF coils. 
     
     
       21. The method of  claim 19  further comprising the step of constructing the first and the second RF coils in parallel with one another. 
     
     
       22. The method of  claim 21  further comprising the step of constructing the inductor assemblies such that the mutual inductance therebetween decreases as a distance between the first RF coil and the second RF coil increases, and such that the mutual inductance therebetween increases as the distance between the first RF coil and the second RF coil decreases. 
     
     
       23. The method of  claim 19  further comprising the step of constructing the first and the second RF coils to rotate relative to one another about an axis of rotation. 
     
     
       24. The method of  claim 23  further comprising the step of constructing the inductor assemblies such that the mutual inductance therebetween increases as a relative angle between the first RF coil and the second RF coil increases, and such that the mutual inductance therebetween decreases as the relative angle between the first RF coil and the second RF coil decreases.